The valves of an internal combustion engine cooperate with valve seats at the surface of the cylinder head to create a seal within the chamber to contain the expanded gases within the chamber. The integrity of the seal is critical to smooth, efficient operation of the engine. Further, the valve seat must be smooth and clear on its inner surface to allow unobstructed gas flow when the valve is open. Due to mechanical failures, improper operation of the engine, or wear, the valve seats can be damaged, causing the seal integrity to be compromised. While the valve seat can be replaced, the more common practice is to machine the valve seats to restore the smooth surface required for efficient operation. Devices for machining valve seats include a rotary cutting or grinding tool which is typically made of tungsten carbide that is connected to a rotating spindle centered within the valve seat. Centering of the cutting or grinding edge is important since the seat face must be concentric with the axis of the valve and the valve guide, and the seat must be perfectly round. To maintain the tool in an orientation that is centered with respect to the valve seat the device uses a rod, commonly known as a pilot, that extends downwardly from the center of the spindle into the valve guide and rotates with the spindle. The pilot is typically made of tungsten carbide for wear resistance. The same tool may also be used for machining the valve seat housing if the valve seats are to be replaced.
Valve seat machining devices known in the art are difficult to align precisely. The pilot is retained in a bore in the center of the spindle by a set screw. Because the bore must have a slightly larger diameter than the portion of the pilot that is retained within it, the portion of the pilot that extends through the valve guide may be slightly off-axis with respect to the central axis of the valve guide. Misalignment of the pilot causes misalignment of the cutting tool on the valve seat and may also stress the pilot.
In addition, valve seat machining devices known in the art are uneconomical. The engines of different manufacturers typically have valve guides of different diameters. Distributors, retailers and persons who regularly repair engines must therefore maintain an inventory of pilots covering the entire range of diameters. The pilots are expensive because they must be formed to precise tolerances and are made of costly materials such as tungsten carbide.
It would be desirable to provide a valve seat machining device that reduces the number of different pilots that must be maintained in an inventory. It would also be desirable for the device to facilitate alignment of the pilot in the spindle. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.